Marthasterias, Jullien, 1878

Mah, Christopher & Foltz, David, 2011, Molecular phylogeny of the Forcipulatacea (Asteroidea: Echinodermata): systematics and biogeography, Zoological Journal of the Linnean Society 162 (3), pp. 646-660 : 655-656

AND MARTHASTERIAS

The New Zealand species Sclerasterias mollis and the South Australian/South Pacific Australiaster were supported on both the two-gene and three-gene trees with 100% bootstrap support. The sister clade to the Sclerasterias mollis + Australiaster lineage included Rumbleaster and two Atlantic Sclerasterias species , Sclerasterias contorta and Sclerasterias eustyla . In both trees, all members of the Sclerasterias clade are strongly supported with 100% bootstrap support.

Australiaster and Rumbleaster possess few morphological distinctions from Sclerasterias , which compels us to conclude that they are synonyms of Sclerasterias . Sclerasterias (including Rumbleaster and Australiaster ) includes 14 species ( Clark & Mah, 2001), which are present in the Atlantic, Pacific, and Indian Oceans, occurring at continental shelf, upper bathyal depths of approximately 20– 700 m. The genus Sclerasterias is unusual as a primary clade within the Asteriidae in that it shows relatively conservative morphology (i.e. all members of the genus Sclerasterias are recognizable), but includes species from a widespread distribution.

Sclerasterias has been collected in shallow-water (i.e. littoral) sediments from the Eocene of Seymour Island ( Blake & Zinsmeister, 1979, 1988), but has not been recorded from the modern Antarctic fauna, although some species are recorded from the South Atlantic and sub-Antarctic regions (e.g. Bernasconi, 1979). Sclerasterias species are not known from the Arctic.

The phylogenetic placement of Rumbleaster within the Sclerasterias clade adds an unusual environmental association to the phylogeny. This lineage includes two of the few asteroid species known to occur in association with cold seep-type chemosynthetic communities in two different oceanic regions. Sclerasterias tanneri in the Gulf of Mexico has been described as a ‘colonist’- type member of a chemosynthetic system ( Carney, 1994), with species obtaining 50–100% of their nutrition from cold-seep production ( MacAvoy et al., 2002). More recently ‘ Rumbleaster ’ (= Sclerasteria s) eructans was described from the Rumble submarine volcanoes in the Bay of Plenty, New Zealand ( McKnight, 2006), where it was observed feeding on the Bathymodiolus -like mytilid mussel Gigantidas gladius ( vonCosel & Marshall, 2003). Feeding habits for other species of Sclerasterias have not been reported, but only one species ( Sclerasterias mollis ) occurs in relatively shallow water ( Clark & Mah, 2001), with the remaining species known to occur as deep as 700 m. The phylogenetic significance of this association is unclear, but is presented here as an encouragement towards further study.

The widely distributed Atlantic asteriid Marthasterias occurs as the sister group to the Sclerasterias lineage in our three-gene tree, but not in our two-gene tree. Our two-gene tree places Marthasterias as the sister lineage to the entire Asteriidae clade. Neither of these relationships was well-supported (if at all) by bootstrap values.

PHYLOGENY AND FOSSIL FORCIPULATACEA: